This CPD is sponsored by VMZINC. It aims to help specifiers gain knowledge about the use of zinc products in the construction process. This CPD explores the science behind the products and the benefits of using zinc.
VMZINC is the international brand name of rolled zinc products manufactured and sold by the Building Products Unit of Umicore. VMZINC, a leader in the French and Belgian markets and established in 15 countries worldwide, offers a range of roofing products and systems, façade cladding, rainwater systems and ornaments.
Part 1: Zinc Production and History
A Zinc is the 23rd most common element found in the earth’s crust. It has been used in carious forms for over 2000 years. In the 18th century the first large-scale zinc production began in Bristol.
The Société des Mines et Fonderies de Zinc de la Vielle Montage was founded in 1837 and prospered under the Haussmannian re-development of Paris. Zinc was also used on a number of buildings in the UK during the 19th century including stations along the Great Western Railway.
To create zinc panels and sheets 99.995 per cent pure-zinc cathodes are melted in an oven with small amounts of copper and titanium. The zinc is then hot rolled into a 9–16mm thick initial slab. This is then rolled down to the standard thicknesses of 0.7, 0.8, 1 and 1.5mm
Part 2: Aesthetics of Zinc
Zinc will react with water to form zinc hydroxide, and then with carbon dioxide to form zinc hydroxy carbonate. This is a slow process that may take up to 10 years, but gives zinc its distinctive grey patina. Since 1978, investment and innovation in pre-weathering techniques have meant that there are now a number of finishes and coatings available that allow for different aesthetic possibilities.
There are three fundamental ways to join zinc panels:
• Standing seam joint
• Flat lock joint
• Reveal joint
The choice of panel and joint can provide articulation across a surface or a more planar finish.
Part 3: Available Systems
There are two main systems for installing zinc roofing: batten cap and standing seam.
Batten cap roofing
This is the traditional method of installing a zinc roof using a U-shaped panel, timber battens and cover flashing.
Standing seam roofing
Panels can be up to 600mm wide and 13m in length. This system can be used to clad most shapes, including curves. It must be installed over a continuous substrate, then crimped to form a joint. For standing seam wall cladding, panels 430mm wide and no longer than 4m in length are recommended. Thickness should be 0.8mm for cladding (generally 0.7mm for roofing). Zinc hanging and internal gutters can be used with zinc as well as slate and tile roofs.
The options available for walls are more varied and include flat lock shingles. Interlocking panels and other larger format rainscreen wall systems include cassettes made from zinc composite material.
Part 4: Performance
Zinc is 100 per cent recyclable and in Western Europe 98 per cent is recycled and reused. BRE analysis found that zinc products have a lifespan of at least 80 years and require very limited maintenance, thus offering many systems with a Green Guide rating of A+. Traditional vented systems such as standing seam and flat lock panels follow a Code of Practice (143-5:1964) and are acceptable to the National House Building Council. BBA certificates exist for non-vented warm roof build-ups. Many zinc rainscreen systems are Centre for Window and Cladding Technology tested by UK-based fabricators that test water penetration, wind resistance serviceability/ safety, hard and soft impact.
Part 5: Procurement and Budget
Zinc is stocked in the UK in sheet, coil and gutter form. Overlapping panels can be bought off the shelf and installed for less than £100/m2(including support rails). Other more bespoke systems can have a lead time of up to 12 weeks. Standing seam roofs will have an approximate supply and fit price of around £100/m2whereas complex rainscreen zinc composite material clad walls maybe nearer to £400/m2.
Part 6: Other Systems
Zinc can be perforated in order to create patterns and for solar shading devices, however the maximum open area should not exceed 50 per cent. Photovoltaic panels can easily be fitted to standing seam roof panels, however care must be taken in allowing for increased loading from the weight of the panels combined with wind and snow loads. Internally, systems that use rails and magnets allow for easy installation and removal of zinc panels. Since zinc was first used as a roofing material almost 200 years ago, it has also been used to create roofing ornaments ranging from simple finials to complex domes..